Ankle-Brachial Index (ABI) Calculator
Enter systolic blood pressure values in mmHg. This tool uses the standard method: highest ankle pressure for each leg divided by highest brachial pressure from either arm.
The Ankle-Brachial Index (ABI) is a simple, non-invasive screening tool used to evaluate blood flow in your legs. It compares blood pressure measured at the ankle to blood pressure measured at the arm. A lower ABI may suggest peripheral artery disease (PAD), a condition where arteries in the legs become narrowed and reduce circulation.
What is ABI and why does it matter?
ABI is widely used in primary care, cardiology, vascular clinics, and preventive health settings. Because PAD can be silent in its early stages, ABI helps detect problems before severe symptoms appear. It can also support risk assessment for broader cardiovascular conditions, since PAD is associated with increased heart attack and stroke risk.
Clinical uses of ABI include:
- Screening people with leg pain when walking (claudication)
- Evaluating non-healing foot wounds
- Monitoring known peripheral artery disease over time
- Assessing vascular status before certain procedures or exercise programs
How this ABI calculator works
The standard calculation uses:
ABI = (highest ankle systolic pressure in one leg) / (highest brachial systolic pressure from either arm)
You calculate one ABI for each leg:
- Right ABI = max(right dorsalis pedis, right posterior tibial) / max(right arm, left arm)
- Left ABI = max(left dorsalis pedis, left posterior tibial) / max(right arm, left arm)
The lower of the two leg values is often used for overall risk interpretation.
ABI interpretation guide
| ABI Range | Typical Interpretation |
|---|---|
| > 1.40 | Non-compressible arteries (possible calcification; further testing may be needed) |
| 1.00 to 1.40 | Normal |
| 0.91 to 0.99 | Borderline |
| 0.70 to 0.90 | Mild PAD likely |
| 0.40 to 0.69 | Moderate PAD likely |
| < 0.40 | Severe PAD likely / critical ischemia concern |
Step-by-step measurement tips
Before taking readings
- Let the patient rest lying down for at least 5 to 10 minutes.
- Avoid smoking, caffeine, and exercise shortly beforehand when possible.
- Use a properly sized blood pressure cuff.
During measurement
- Record systolic pressure in both arms.
- Measure dorsalis pedis and posterior tibial systolic pressure in both ankles (usually with Doppler).
- Use the highest brachial pressure as the denominator for both legs.
- Use the higher ankle vessel pressure for each leg as the numerator.
When ABI can be misleading
In some patients, especially those with diabetes, chronic kidney disease, or advanced age, arteries may be stiff or calcified and difficult to compress. This can produce unusually high ABI values (often above 1.40), even when disease is present.
In these cases, clinicians may order additional tests such as:
- Toe-brachial index (TBI)
- Duplex ultrasound
- Pulse volume recordings
- Exercise ABI testing
Who should consider ABI assessment?
- Adults with exertional calf, thigh, or buttock discomfort
- People over age 65
- People over age 50 with diabetes or smoking history
- Patients with known atherosclerotic disease in other vascular beds
Bottom line
An ABI calculator is a fast way to transform raw blood pressure readings into meaningful vascular insight. Used correctly, it helps flag potential peripheral artery disease early and supports better cardiovascular prevention. Save your readings, track changes over time, and combine ABI with professional clinical assessment for the most accurate interpretation.